While the tone of "Harrison Bergeron" is detached and sarcastic, the mood changes to reflect the reader's response to the action—it starts out curious, builds to a crescendo of excitement and hope as Harrison makes his stand, and then bursts into resigned dismay after he's stopped.
The tone of the story is reflected in the way the author writes. Kurt Vonnegut takes a detached tone in his writing, describing the situation as if it's normal—when, of course, it isn't normal for a reader. He explains that society made everyone equal by instituting handicaps that kept people from excelling in any way. It made things fair for everyone.
The sarcastic tone comes largely from the ludicrous way people have been made equal; Vonnegut doesn't directly criticize it, leaving the reader to make their own decisions. There's also a sardonic tone with the way Vonnegut writes Hazel and George. George argues against Hazel's desire for him to lighten his handicaps just a little at home—saying that it would return society to the dark ages when no one was equal.
The reader's mood starts from a place of curiosity as Vonnegut describes the society and the handicaps that George has: a loud sound that goes through an earpiece every few minutes to keep him from being able to think clearly and dozens of pounds of buckshot in a bag around his neck. His wife, Hazel, doesn't have these. Vonnegut exposes this society through George, Hazel, and their television program. The novel situation arouses curiosity in a reader—even as the reader knows this is not a healthy society.
When Harrison bursts into the room on television and disrupts the ballet, the quick action and his desire for freedom cause the reader to experience hope alongside him—which leads to excitement. The question of whether he'll change things keeps the reader excited throughout Harrison's display. The action rises when the ballerina joins him and the musicians begin to play with skill.
The reader's excitement and hope are cut short when Diana Moon Glampers comes in and quickly kills Harrison and the ballerina. Dismay is tempered with resignation when George and Hazel can no longer see what's happened, because the television tube burns out after Harrison is killed. The reader sees that nothing has changed, as even Harrison's parents forget and ignore what happened.